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Possible mechanism of ciliary stimulation by extracellular ATP: Involvement of calcium-dependent potassium channels and exogenous Ca2+
Authors:T. Weiss  L. Gheber  V. Shoshan-Barmatz  Z. Priel
Affiliation:(1) Department of Life Sciences, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel;(2) Department of Chemistry, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel
Abstract:Summary Ciliary motility was examined optically in tissue cultures from frog palate epithelium and frog's esophagus as a function of extracellular concentration of adenosine 5prime-triphosphate (ATP) and related compounds. The addition of micromolar concentration of ATP caused a strong enhancement of frequency and wave velocity in the direction of the effective stroke. Since adenosine 5prime-[beta,gamma imido]-triphosphate (AMP-PNP), a nonhydrolyzable analog of ATP, produces the same effects, ATP hydrolysis is not required. The overall potency is ATP cong AMP-PNP>ADP Gtadenosine>AMP. It is suggested that both the phosphate and the base moieties are involved in ATP binding.The enhancement of ciliary activity by extracellular ATP is dependent on the presence of extracellular Ca2+, which can be replaced by extracellular Mg2+. The effect of a number of potent inhibitors of the voltage-gated calcium channels on the stimulation of ciliary activity by ATP were examined. No effect was detected in the concentration range within which these agents are specific. On the other hand, quinidine, a potent inhibitor of K+ (calcium-dependent) channels, inhibits the effect of ATP.The following model is suggested: exogenous ATP interacts with a membrane receptor in the presence of Ca2+, a cascade of events occurs which mobilizes intracellular calcium, thereby increasing the cytosolic free Ca2+ concentration which consequently opens the calcium-activated K+ channels, which then leads to a change in membrane potential. The ciliary response to these changes is the enhancement of ciliary activity.This work was supported by a grant from the Fund for Basic Research administered by the Israel Academy of Science and Humanities.
Keywords:extracellular ATP  ciliary activity  K+(Ca2+) channels  quinidine  Ca2+ channels
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